Field of the Invention
The present invention relates to a toner used in an image-forming method in the manner of electrophotography, electrostatic recording and toner jet printing.
Description of the Related Art
Image-forming methods used to develop electrostatic latent images are applied to photocopiers, multifunction copiers, and printers. These image-forming methods typically include forming an electrostatic latent image on a photosensitive member followed by forming a toner image by developing the electrostatic latent image using toner, transferring the toner image to a transfer material in the manner of paper and then fixing the toner image on the transfer material by a fixing method using heat and pressure to obtain a fixed image.
Various methods have been developed for fixing a toner image to a transfer material in the manner of paper. Examples of such methods include a heated roller fixing method whereby a toner image is fixed to a transfer material by heated rollers and pressure rollers, and a film fixing method whereby a pressure member is adhered to a heating unit through a film followed by fixing a toner image to a transfer material.
These fixing methods have favorable thermal efficiency during melt adhesion of a toner image to a transfer material since contact is made between the heated rollers, film surface and toner image on the transfer material, thereby enabling fixation to be carried out rapidly. Consequently, these fixing methods are widely used in multifunction copiers and printers.
Image-forming apparatuses are being strongly required to save energy. One example of an effective means for reducing the energy consumed by image-forming apparatuses is to lower the set temperatures of the heated rollers, film and other fixing members. In order to accomplish this, however, the low-temperature fixability of the toner used has to be further improved. One method that has been proposed for improving the low-temperature fixability of toner includes further lowering the softening point of the toner by using a crystalline resin. As a result of adopting these countermeasures, it has become possible to utilize the sharp melt property attributable to crystalline resin which allows the softening temperature of the toner to be set to a lower temperature, thereby making it possible to improve low-temperature fixability.
However, the above-mentioned toner is susceptible to the occurrence of offset phenomenon in which a portion of the toner (and particularly crystalline resin having low viscosity) ends up adhering to the surfaces of these fixing members and toner adhered to the heated rollers or film ends up re-transferring to the next transfer material. In response to this problem, the use of crystalline and amorphous block resins as binder resins has been proposed (see Japanese Patent Application Laid-open No. S62-273574). As a result of implementing these countermeasures, offset to fixing members decreases and a toner can be obtained that has stable fixing performance over a wide temperature range.
However, at present, with the growing proliferation of multifunction copiers and fax machines and printers and their use in various regions and environments, new problems have arisen involving the occurrence of image defects as a result of being unable to obtain favorable charging characteristics when conventional toner is used under more diverse conditions.
In addition, as the functions of multifunction copiers and printers have become increasingly sophisticated, in multifunction copiers and printers that require continuous and high-speed printing over a long period of time, in a case where continuous printing is carried out using conventional toner, the toner ended up melt-adhering to the developing device as a result of being unable to obtain adequate durability, and this ended up causing the occurrence of image defects.
Consequently, there is a need for a toner that demonstrates superior low-temperature fixability and allows the formation of favorable toner images over a long period of time while maintaining a wide fixable range.